1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
An electrophotographic method has been widely adopted in known image forming apparatuses, such as a copying machine, a printer, and a facsimile. In the electrophotographic method, it is general that a photoreceptor having a photosensitive layer, which includes photoconductive substances, formed on a surface thereof is used, charges are applied to the surface of the photoreceptor in order to uniformly charge the surface of the photoreceptor, an electrostatic latent image corresponding to image information is formed in various kinds of image forming processes, the electrostatic latent image is developed with a developer containing toner supplied from a developing section so as to make a toner image, and the toner image is directly transferred onto a recording medium, such as paper, or is first transferred onto an intermediate transfer medium and is then transferred onto a recording medium to thereby form an image. In addition, in order to fix the toner image, which is transferred onto a recording medium, on the recording medium, it is general to apply heat and pressure to the recording medium by a fixing section in a heat fixing method, such as a developing roller. In the heat fixing system, it is necessary to heat toner at high temperature of about 150° C. in order to soften and fuse the toner by using a heating apparatus, such as a heater. Accordingly, the power consumption increases. It is a present condition that about a half or more of total power consumption in an electrophotographic image forming apparatus occurs due to the heat fixing. On the other hand, energy saving activities have been progressing to stop global warming. This is also related to universal use of electrophotographic image forming apparatuses. Accordingly, even in the electrophotographic image forming apparatuses, it is requested to reduce the power consumption.
As a solution to the problem described above, there is known a wet fixing method of using a fixing fluid containing water and liquid that can be dissolved or dispersed in water and act to soften or swell toner or resin components of toner. In the wet fixing method, a softened or swollen toner image is adhered onto a recording medium by supplying the fixing fluid and then the toner image is fixed onto the recording medium by applying pressure. Since toner is softened or swollen due to a fixing fluid and is then fixed in the wet fixing method, the power consumption in the wet fixing method is much smaller than that in the heat fixing method. For this reason, various kinds of proposals for improvements of the wet fixing method have been made. For example, there has been proposed an electrophotographic image forming apparatus that has a toner image forming section and has a configuration in which a toner image formed by the toner image forming section is directly transferred onto a recording medium or transferred onto the recording medium through an intermediate transfer medium (for example, refer to Japanese Unexamined Patent Publication JP-A 2-167761 (1990)).
In the image forming apparatus, the toner image forming section includes a fixing fluid holding member, a fixing fluid supplying section, and developing section. In addition, an image composed of a fixing fluid corresponding to image information is formed on the fixing fluid holding member by means of the fixing fluid supplying section, and a toner image is formed by supplying toner to the image by means of the developing section. Further, there has been proposed an image forming method in which an image is formed by discharging liquid having viscosity onto a recording medium in an inkjet method in accordance with image information and then a final image is formed by adhering a coloring agent onto the image (for example, refer to Japanese Unexamined Patent Publication JP-A 9-216351 (1997)). Furthermore, there has been proposed an image forming method in which an image is formed by discharging a fixing fluid onto a recording medium in an inkjet method in accordance with image information and then a final image is formed by adhering toner onto the image (for example, refer to Japanese Unexamined Patent Publication JP-A 9-216453 (1997)). Furthermore, there has been proposed an image forming apparatus which has an inkjet type fixing fluid supplying section and a developing section and in which liquid droplets are discharged from the inkjet type fixing fluid supplying section onto a recording medium or an intermediate transfer medium in accordance with image information so as to form an image composed of a fixing fluid on the recording medium or the intermediate transfer medium and then toner is supplied to the image by means of the developing section so as to form a toner image (for example, refer to Japanese Unexamined Patent Publication JP-A 2000-168058). The image forming apparatus includes a toner removing section for attracting and removing toner, which is excessively supplied from the developing section onto the recording medium or the intermediate transfer medium, by an electrostatic force and a toner recovering section for returning toner removed by the toner removing section to the developing section.
In the known techniques described above, the fixing fluid is supplied to a recording medium or the like by using the inkjet method. However, in order to do so, it is necessary to lower the viscosity of the fixing fluid and to make an adjustment to a viscosity range where the fixing fluid can be discharged in the inkjet method. In addition, in the case of causing a fixing fluid having low viscosity to be adhered onto a recording medium, such as normal paper, the fixing fluid permeates into a part (non-image part) other then a corresponding image in a region where the fixing fluid image is formed. As a result, blur easily occurs. In addition, since the entire fixing fluid that is supplied cannot be used to soften and swell toner, an efficiency of transfer of a toner image onto a recording medium or the like is worse. In the case of raising the viscosity in order to prevent the permeation of the fixing fluid, it takes time to discharge the fixing fluid by using the inkjet method. Moreover, there is no explanation on a practical and effective method for preventing toner from permeating into or being adhered onto a non-image part when forming a fixing fluid image corresponding to image information other than a solid image.
Further, there has been proposed an image forming apparatus that includes a photoreceptor that bears an electrostatic latent image on a surface thereof, a developing roller that supplies toner to the photoreceptor, an electric potential applying roller that forms a liquid developer layer, in which toner is dispersed in insulating liquid, on a surface of the developing roller, and a developer tank that supplies liquid developer to the electric potential applying roller and performs liquid development (for example, refer to Japanese Unexamined Patent Publication JP-A 9-62109 (1997)). The liquid developer is adhered onto a surface of the electric potential applying roller when the electric potential applying roller is rotated under a state in which a part of the electric potential applying roller is immersed in the liquid developer contained in the developer tank. Then, the electric potential applying roller applies an electric potential to the liquid developer so as to charge toner in the liquid developer with an electric potential higher than the surface of the developing roller. Then, toner and insulating liquid adhered onto the toner in a part where the electric potential applying roller and the developing roller are positioned to be closest to each other are adhered onto the surface of the developing roller due to an electrophoretic phenomenon, such that a liquid developer layer is formed on the surface of the developing roller. In a part where the developing roller and the photoreceptor are positioned to be closest to each other, toner is supplied from the liquid developer layer of the developing roller to an electrostatic latent image on the photoreceptor, and thus the electrostatic latent image is developed. In order to perform electrophoresis by charging toner like liquid developing, a large amount of insulating non-aqueous solvent should be used. However, in the case of using a large amount of non-aqueous solvent, it is necessary to prepare a container, which is used to recover the non-aqueous solvent, inside the image forming apparatus, which causes increase in the size of an image forming apparatus. In addition, since the non-aqueous solvent smells very bad, it is not possible to prevent bad smell from leaking. Accordingly, it is difficult to dispose an image forming apparatus that performs liquid developing within doors.